For Conscience Sake? For Goodness Sake?

Style guides disagree on whether to make “for conscience’s sake” and similar terms possessive.

The Chicago manual of style considers these “for blank’s sake” expressions to be possessive, so according to Chicago you would put an apostrophe and S after “conscience” in “conscience’s sake.” But the guide makes an exception for expressions like “for goodness’ sake” where the word before sake ends in an S. here, Chicago feels, you should add just an apostrophe but no additional S because otherwise you’d have too many Ss run together.

The “Associated Press Stylebook,” however, says that for these figures of speech, you add just an apostrophe.